Minimally-invasive cardiac-valve prosthesis

ABSTRACT

A cardiac-valve prosthesis is adapted for percutaneous implantation. The prosthesis includes an armature adapted for deployment in a radially expanded implantation position, the armature including a support portion and an anchor portion, which are substantially axially coextensive with respect to one another. A set of leaflets is coupled to the support portion. The leaflets can be deployed with the armature in the implantation position. The leaflets define, in the implantation position, a flow duct that is selectably obstructable. The anchor portion can be deployed to enable anchorage of the cardiac-valve prosthesis at an implantation site.

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority from Italian patent application numberTO2004/A000135, filed on Mar. 3, 2004, which is hereby incorporated byreference.

TECHNICAL FIELD

The present invention relates to cardiac-valve prostheses. Morespecifically, the present invention is directed to a prosthesis that isamenable to minimally-invasive implantation.

BACKGROUND

Recently, there has been increasing consideration given to thepossibility of using, as an alternative to traditional cardiac-valveprostheses, valves designed to be implanted using minimally-invasivesurgical techniques or endovascular delivery (the so-called“percutaneous valves”). Implantation of a percutaneous valve (orimplantation using thoracic-microsurgery techniques) is a far lessinvasive act than the surgical operation required for implantingtraditional cardiac-valve prostheses. Further details of exemplarypercutaneous implantation techniques are provided in U.S. Publication2002/0042651, U.S. Pat. No. 3,671,979, and U.S. Pat. No. 5,954,766,which are hereby incorporated by reference.

These prosthetic valves typically include an anchoring structure, whichis able to support and fix the valve prosthesis in the implantationposition, and prosthetic valve elements, generally in the form ofleaflets or flaps, which are stably connected to the anchoring structureand are able to regulate blood flow.

Furthermore, the methods of implantation of valves via a percutaneousroute or by means of thoracic microsurgery are very frequentlyirrespective of the effective removal of the natural valve leaflets.Instead, the cardiac valve may be introduced in a position correspondingto the natural annulus and deployed in situ by simply divaricatingdefinitively the natural valve leaflets.

There is a need for a percutaneous valve that does not run the risk ofbeing displaced (dislodged) with respect to the implantation position,as a result of the hydraulic thrust exerted by the blood flow. There isa further need for a percutaneous valve that secures tightly to the flowduct generally defined by the natural valve annulus, such that itresists blood flow around the outside of the percutaneous valvestructure.

SUMMARY

In an exemplary embodiment, the invention described herein is based onthe concept of separating, in the framework of the supporting armatureof the valve, the function of anchorage of the valve in the implantationsite (including the possible function of sealing the valve with respectto the blood-flow duct natural to the region in which the valve isimplanted) and the valve function proper. In a preferred way, thispurpose is achieved by providing, within the armature of the valve, twostructures (which are functionally distinct, but which in effect may bestructurally integrated with one another), which are delegatedseparately to the accomplishment of these two functions. These twostructures or portions comprise an external portion which can be spreadout to enable anchorage of the cardiac-valve prosthesis at theimplantation site, and an internal portion, which is substantiallyaxially coextensive with the external portion, for supporting theprosthetic valve leaflets. The valve thus obtained is adapted in aparticularly advantageous way to be implanted in a positioncorresponding to the so-called Valsalva's sinuses.

While multiple embodiments are disclosed, still other embodiments of thepresent invention will become apparent to those skilled in the art fromthe following detailed description, which shows and describesillustrative embodiments of the invention. As will be realized, theinvention is capable of modifications in various obvious aspects, allwithout departing from the spirit and scope of the present invention.Accordingly, the drawings and detailed description are to be regarded asillustrative in nature and not restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a general perspective view of a prosthetic valve according tothe invention.

FIG. 2 illustrates the corresponding armature of the valve without theleaflets.

FIGS. 3 and 4 illustrate a second exemplary embodiment of a prostheticvalve according to the invention.

While the invention is amenable to various modifications and alternativeforms, specific embodiments have been shown by way of example in thedrawings and are described in detail below. The intention, however, isnot to limit the invention to the particular embodiments described. Onthe contrary, the invention is intended to cover all modifications,equivalents, and alternatives falling within the scope of the inventionas defined by the appended claims.

DETAILED DESCRIPTION

In the figures, the reference number 1 designates as a whole a cardiacvalve, which can be implanted via percutaneous route or resorting tothoracic-microsurgery techniques. These percutaneous implantationtechniques are generally known in the art, and include those techniquesdescribed in the documents referenced above.

The valve 1 represented in FIGS. 1 and 2 is basically made up of twoelements, namely an armature 2, having the characteristics that emergemore clearly from the representation of FIG. 2, and a set of leaflets 3,coupled to the armature 2. The characteristics of the leaflets 3 may beappreciated more fully from the view of FIG. 1.

As shown in FIG. 2, the armature 2 of the valve has a general cage-likestructure comprising a set of ribs that extend with a general symmetryof a cylindrical type about a principal axis X4. In percutaneous valves,the axis X4 usually corresponds to the principal axis of the distal partof the catheter used for implantation of the valve 1. For the presentpurposes, the axis X4 can be viewed basically as an entity of a purelygeometrical nature, even though it can in effect be identified eitherwith elements of the implantation catheter or with elements of thearmature 2 of the valve 1.

The armature 2 includes a distinguishable first and a second series ofribs designated, respectively, by the reference numbers 5 and 6. Theseribs are usually made of metal material that is able to presentcharacteristics of radial expandability, both as a result of a positiveaction of a dilatation or divarication force exerted by, for example, aballoon catheter and as a result of characteristics proper to thematerial constituting the ribs 5 (and possibly 6). In particular, theribs may be made of a superelastic material and/or a material withshape-memory characteristics. A material that is well known inbiomedical applications and that presents these characteristics is thematerial known as Nitinol.

Structures that may substantially be likened to cages, which can beintroduced into a vessel of the human body and in particular into avenous site and can then be dilated in loco via dilatation of a distalpart of the introducing catheter or, in the case of materials withshape-memory characteristics or the like, as a result of the retractionof a sheath that maintains the structure in a compressed position, arewell known in the art. For example, these structures are well known instent technology and, in particular, the technology of stents forangioplasty.

Due to the possibility of providing cage-like structures with ribsextending with a profile more or less shaped in diametral planes withreference to a principal axis, such as for example the axis X4, furtherreference may be made to technologies adopted for the fabrication ofdevices for the mapping or passivation of endocardial sites, such as,typically, endocavitary sites, used for localization and/or treatment ofthe so-called ectopic sites characteristic of the pathologicalconditions of a fibrillative type.

The distinction made between the ribs 5 and 6 is based on the fact that,within the armature 2, these different sets of ribs are designed toperform different functions, regardless of whether the ribs constitutephysically distinct parts or are different portions of a unitarystructure within the armature 2. In particular, the ribs 5 form anexternal part or anchor portion of the armature 2 designed (see FIG. 1)to enable the location and anchorage of the valve 1 at the implantationsite. The ribs 6 are designed to constitute a more internal part orsupport portion of the armature 2, specifically the part that is tosupport the valve leaflets 30 of the prosthesis. Essentially, the ribs 5and 6 are designed to define, within the armature 2, an external portion(ribs 5), which can be spread out or radially expanded to enableanchorage of the prosthesis 1 in the implantation site and an internalportion (ribs 6), which supports the prosthetic valve leaflets 30provided in the set of leaflets 3.

An important characteristic of the solution described herein is providedby the fact that the two portions of the armature 2 are “substantiallyaxially coextensive” with respect to one another. This definition isunderstood to indicate synthetically the fact that the two portionsoccupy, in the direction of the axis X4, axial stretches that aresubstantially coincident with one another. This is in direct contrastwith solutions such as the one described, for example, in the U.S. Pat.No. 6,482,228, which illustrates a valve comprising two homologousportions that are totally staggered with respect to one another in anaxial direction so that they can be located, one in a proximal positionand the other in a distal position with respect to the coronary ostia.

The ribs 5, which in what follows are designated also as “external”ribs, are preferably arranged in sets of ribs, said sets being typicallyarranged in threes or multiples of three so as to be more readilyadaptable, in a complementary way, to the anatomy of the Valsalva'ssinuses, which is the site of choice for implantation of the valve 1.

In an exemplary embodiment, within the ribs 5 there is distinguishable atop part or top branch 50 and a bottom part or bottom branch 51. In theimplantation position, the top parts or branches 50 are able, when theyare in the deployed or expanded position, to extend within the so-calledValsalva's sinuses. The Valsalva's sinuses are the dilatations, from theoverall lobed profile, which are present at the root of the aorta, hencein a physiologically distal position with respect to the aortic valveannulus. The bottom portions or branches 51 (see FIG. 1) are insteaddesigned to extend in a proximal position with respect to the valveannulus so as to extend for a certain stretch within the ventricularchamber.

As a whole, the top parts 50 of the ribs 5, when brought into theextended position, jointly define a tripodal structure, which, byexpanding within the Valsalva's sinuses, enables attainment of acondition of firm anchorage of the valve 1. This avoids the possibilityof the valve 1, once implanted, being dislodged or even just displacedwith respect to the implantation position, as a result of the hydraulicstresses applied thereto during operation by the blood flow.

The anchorage of the valve 1 in the implantation site is furtherreinforced by the fact that the area of radiusing between the topbranches 50 and the bottom branches 51 of the ribs 5 has, precisely onaccount of the general divaricated or flared pattern of the bottombranches 51, an area of convexity that is thus positioned astride of thevalve annulus, reinforcing the condition of shape fit between thearmature of the valve and the implantation site. In the schematicrepresentation of the figures, the natural valve leaflets of the valvethat is to be replaced with the prosthetic valve 1 are not specificallyillustrated.

The valve 1 described herein can be located in situ regardless ofwhether the natural valve leaflets have previously been removed or (andin a way that is from certain points of view preferred), withoutproceeding to the removal of said natural valve leaflets, by simplyintroducing the valve within the valve orifice and thus bringing about,as a result of the divarication of the valve 1 structure, thecorresponding definitive divarication of the natural valve leaflets thatare brought into, and maintained in, a position of substantial adherenceto the surrounding portion of the valve annulus.

The particular conformation of the ribs 5, and in particular of theparts 50 and 51 just described, corresponds to the solution envisagedfor the implantation of the valve 1 in the aortic site. Similarstructures can be adopted for implantations, for example, in the mitralsite.

The top and bottom branches 50 and 51 may in actual fact presentconformations that are altogether different from the ones illustrated.For example, the top branches 50 may possibly present a conformationthat is approximately symmetrical to the conformation represented hereinwith reference to the bottom branches 51, thus conferring on theexternal part of the armature of the valve 2 an overall hourglassconformation. Moreover, the presence of both of the branches 50 and 51is altogether optional.

Again, in the exemplary embodiment illustrated herein, the terminal topends of the branches 50 and the bottom ends of the branches 51 areconnected to collar parts 52, which are designed to be fitted around,and usually to slide along the principal axis X4 during divarication ofthe armature 2. This solution proves advantageous as regards to thesimplicity and the structural congruence of the armature 2. Recoursethereto should, however, be reconciled with the need to prevent thecollar parts 52 from possibly ending up playing an excessive role ofobstruction in regard to the blood flow that is to pass (from belowupwards, with reference to the configuration of implantation asrepresented in FIG. 1) through the central orifice of the valve 1defined between the valve leaflets 30 in a divaricated position. Forexample, it is conceivable to use just one of the collars 52, forexample the one illustrated in the bottom portion in FIG. 2.

The structure and the configuration of the ribs 6 is, as a whole, akinto that of the ribs 5. In the case of the ribs 6, which form theinternal part of the armature 2 of the valve 1, there is, however,usually the presence of just three elements that support, in a positioncorresponding to homologous lines of commissure (which take materialform as sutures 31 passing through openings 61 provided on the elements6), the valve leaflets 30. Essentially, the complex of ribs 6 and valveleaflets 30 is designed to form the normal structure of a biologicalvalve prosthesis. This is a valve prosthesis which (in the form that isto be implanted with a surgical operation of a traditional type, henceof an invasive nature) has met with a wide popularity in the art.

The structural details of biological valve prostheses, consisting of atubular structure made of biological material (for example, thepericardium or meningeal tissue of animal origin) subjected totreatments of passivation (with gluteraldehyde or similar compounds) oralternatively a biocompatible synthetic material, after prior possibleshaping of the cusp-like areas that are to constitute the prostheticvalve leaflets 30, are well known in the art. For further details of thestructure of such a valve, reference can be made to EP-B-0 155 245,which is hereby incorporated by reference. For further details of thetechnology of fabrication and/or treatment of the material of theprosthetic valve leaflets, useful reference can be made to EP-B-0 133420, which is hereby incorporated by reference.

In addition to the more strictly “valve” part comprising the prostheticvalve leaflets 30 supported in a commissural position by the ribs 6 ofthe armature 2, the leaflet part of the prosthesis illustrated also hasan apron-like part 32, which extends according to a general chimney-likeor flared configuration and is supported by the bottom parts 51 of theexternal ribs 5 of the armature 2. For this purpose, the bottom parts 51have an overall V-shaped structure, hence comprising two branches thatare to enclose within them the chimney-like portion 32 of the set ofleaflets 3 of the valve armature 2, so causing this to be divaricated atthe moment of spreading out of the valve and maintained in saiddivaricated position in the intraventricular site in a proximal positionwith respect to the valve annulus.

Albeit conserving an extreme structural simplicity, from which therederives a corresponding reliability during implantation, the valvestructure described manages to meet in an excellent way various needsthat in themselves contrast with one another. This is obtained basicallyby separating the two parts of the armature 2, which are functionallydistinct, even though they may be integrated in a single structure, andhence delegating to them two different functions.

In particular, the external ribs 5 (and more specifically when these arepresent in the two branches 50 and 51, which can be positioned astrideof the valve annulus) provide the firm anchorage of the valve in situ,so preventing it from possibly being removed or even just displaced fromthe implantation site chosen by the person carrying out the implantationoperation. This is obtained with a structure that is able to adapt tothe natural anatomical conformation without exerting thereon stresses ofa traumatic nature.

As shown in the Figures, the ribs 5 can present a rather thin or lightstructure. This allows them to adhere to the walls of the root of theaorta, to the surrounding portion of the valve annulus, and to the wallsof the endocardial chamber, without exerting particularly markedstresses on those walls, which—in extreme cases—could even be at thebasis of phenomena of lesions and, even more, of onset of reactions ofthe organism in regard to said lesions. The action of anchorage is infact achieved, more than for any other reason, on account of thepresence of numerous ribs 5 and their conformation, which iscomplementary with respect to that of the implantation site (inparticular, when this is represented by the Valsalva's sinuses).

The internal part of the armature 2, represented by the ribs 6, enables,spreading out and support of the prosthetic valve leaflets 30 in theimplantation position. This is achieved by recourse to a structure and aconformation which, precisely because they reproduce very closely thoseof traditional prosthetic valves of a biological type, proveparticularly suitable and efficient for performing substitution of adefective natural valve. In particular, it is well known that valveprostheses of a biological type, precisely because they are able toreproduce closely the fluid-dynamic characteristics and thecharacteristics of behaviour of the leaflets of natural cardiac valves,can be used to benefit patients affected by forms of rather markedcardiac insufficiency. This possibility is achieved in an optimal way inthe solution described herein precisely because the valve function isrendered altogether independent of the function of anchorage in situ ofthe prosthesis.

The presence of the branches 51 in the armature 2 of the prosthesis and,conversely, of the apron-like or chimney-like portion 32 in the set ofleaflets 3 (in addition to contributing further to the shape fit andhence to the anchorage in the implantation site of the valve 1) likewiseenables very efficient channelling of the blood flow coming from theheart, channelling it in a practically complete way, precisely onaccount of the divaricated or flared configuration of the chimney-likeportion 32 within the flow duct defined within the valve leaflets 30.There is thus minimized (and in effect cancelled out) shortly followingimplantation, the possibility of there being created lines of blood flowthat pass on the outside of the cardiac-valve prosthesis.

The foregoing likewise envisages that the two parts or portions ofarmature 2 are substantially axially coextensive with respect to oneanother, occupying, if viewed in their development in the direction ofthe axis X4, axial stretches substantially coinciding with one another.This characteristic enables a precise positioning of the prostheticvalve leaflets in a “physiological” location (i.e., in a locationbasically corresponding to the location of the natural valve leaflets),likewise benefiting, for the purposes of the anchorage of the prosthesisin situ, from a shape fit with the Valsalva's sinuses.

FIGS. 3 and 4 illustrate a second exemplary embodiment of a cardiacvalve, according to the present invention. From a general structuralstandpoint, the valve of FIGS. 3 and 4 derives basically from thestructure of the valve shown in FIGS. 1 and 2. The valve according toFIGS. 3 and 4 is obtained by recourse, as regards the armature, to asingle element of tubular shape and reticular structure. In particular,FIG. 3 illustrates this tubular element in an “extroverted” or“extended” configuration, whereas in FIG. 4 the same element isillustrated in an “introverted” configuration, corresponding to thefinal conformation of implantation of the valve.

In this particular embodiment, the two parts or portions of the armature2 (the external portion 5 for anchorage of the valve 1 in theimplantation site and the internal portion 6 with the function ofsupporting the valve leaflets) are integrated in a single structureconsisting precisely of the tubular element referred to previously. Thiselement, designated as a whole by reference numeral 2, has asubstantially cylindrical structure that develops about a principal axisX4 and consists of ribs having a general helical conformation andpresenting joints in pairs 53 and 63 at the two ends. The armature 2 iswithout any discontinuity between the external portion 5 and theinternal portion 6 of the ribs. The ribs that form the armature 2 inthis embodiment are basically made of a superelastic material and/orshape-memory material.

The valve 1 passes from the extroverted configuration (FIG. 3) to theintroverted or final configuration (FIG. 4) through a mechanism ofdeformation that may be obtained at the implantation site. This canoccur, in the case of percutaneous valves, via remote manipulationdevices associated to the catheter for introduction of the valve. Saiddevices are in themselves known in so far as they are used inassociation with catheters of various types, for example to obtainactions of selective spreading out of implantation devices, such asstents, stent-grafts or the like.

The mechanism of deployment (i.e., introversion) in question involvespassing from the extended conformation of FIG. 3 to the finalconformation of FIG. 4, thereby causing the joints 63, to which the setof leaflets 3 are fixed (internally with respect to the originalcylindrical tubular element), to converge within the tubular structureand then advance therein until the joints 63 arrive in the proximity ofthe joints 53, which, at the start of the movement of introversiondescribed, were exactly at the opposite end of the original cylindricaltubular element.

Basically, this movement causes the tubular element 2 to pass between anextroverted configuration (FIG. 3), in which said tubular element has asubstantially cylindrical shape, with the external portion 5 andinternal portion 6 of the armature axially juxtaposed with respect toone another, and a final introverted configuration (FIG. 4), in whichthe external portion 5 and internal portion 6 are substantially axiallycoextensive with respect to one another.

This overall movement is usually accompanied by at least a slightdivarication of the joints 53 and of the areas of the armature of thevalve (external part 5) adjacent thereto. This divarication of thejoints 53 and of the areas of the armature adjacent thereto is clearlyperceptible in FIG. 4. In the same figure there is moreover perceptiblethe action of “pinching” of the apron-like part of the leaflet, whichmay be achieved with a positive action of deformation of the armatureand/or by exploiting the shape-memory characteristics of the constituentmaterial. Also in this case, a final configuration is reached, in whichthe external portion 5 and internal portion 6 of the armature 2 of thevalve 1 are substantially axially coextensive with respect to oneanother, finding themselves occupying axial stretches that substantiallycoincide with respect to the axis X4.

In the introverted configuration (see FIG. 4), it is possible todistinguish top branches 50 and bottom branches 51 of the ribs 5, in aconformation suitable for being implanted in the Valsalva's sinuses. Thetop branches 50 extend in a generally cage-like form, which iscomplementary with the lobed anatomy of the Valsalva's sinuses andco-operate with the bottom branches 51, which are to extend in aproximal position with respect to the valve annulus so as to beintroduced within the ventricular chamber, ensuring a firm anchorage ofthe valve 1 at the implantation site. The set of leaflets 3 comprisesthe prosthetic valve leaflets 30 supported by the internal ribs 6 and anapron-like part 32 supported by and fixed to the bottom branches 51 ofthe external ribs 5.

Various modifications and additions can be made to the exemplaryembodiments discussed without departing from the scope of the presentinvention. Accordingly, the scope of the present invention is intendedto embrace all such alternatives, modifications, and variations as fallwithin the scope of the claims, together with all equivalents thereof.

1. A cardiac-valve prosthesis adapted for percutaneous implantation, theprosthesis comprising: an armature adapted for deployment in a radiallyexpanded implantation position, the armature including a support portionand an anchor portion, which are substantially axially coextensive withrespect to one another, the anchor portion and the support portionadapted to assume independent radially expanded configurations when thearmature is in the radially expanded implantation position; and aplurality of leaflets coupled to the support portion, which can bedeployed with the armature in the implantation position, wherein theleaflets define, in the implantation position, a flow duct; wherein theanchor portion can be deployed to enable anchorage of the cardiac-valveprosthesis at an implantation site.
 2. The prosthesis according to claim1 wherein the anchor portion and the support portion of the armature arestructurally distinct from one another.
 3. The prosthesis according toclaim 2 wherein the anchor portion of the armature has a set of ribswhich, in the implantation position, are adapted to conform to a shapeof the implantation site.
 4. The prosthesis according to claim 3 whereinthe ribs have at least one arched portion having an overall archedpattern.
 5. The prosthesis according to claim 4 wherein the ribs of theanchor portion of the armature have a plurality of branches adapted toextend in an endocardial position.
 6. The prosthesis according to claim5 wherein the ribs of the anchor portion of the armature have a convexportion that is adapted to position astride a valve annulus site.
 7. Theprosthesis according to claim 5 wherein the ribs of the anchor portionof the armature include, respectively, a first branch and a secondbranch adapted to extend, respectively, in a distal position and aproximal position with respect to a valve annulus site.
 8. Theprosthesis according to claim 5 wherein the ribs of the anchor portionof the armature are grouped together into three sets, the sets beingspaced generally equidistant about a circumference of the armature. 9.The prosthesis according to claim 1 wherein the support portion of thearmature includes support ribs that are able to support the prostheticvalve leaflets in a commissural position.
 10. The prosthesis accordingto claim 9 wherein the support ribs are grouped together into threesets.
 11. The prosthesis according to claim 1 wherein the armature isobtained from a tubular element comprising ribs having a general helicalconformation.
 12. The prosthesis according to claim 11 wherein the ribsare made of a superelastic material or a shape-memory material.
 13. Acardiac-valve prosthesis adapted for percutaneous delivery andimplantation at an anatomical valve site having a Valsalva sinus, theprosthesis comprising: an armature adapted for delivery in aradially-compressed configuration and deployment in a radially-expandedconfiguration at the valve site, the armature including a supportportion and an anchor portion; and a plurality of leaflets coupled tothe support portion, which can be deployed with the armature in theradially-expanded configuration, wherein the leaflets define a flowduct; wherein the anchor portion includes ribs that in theradially-expanded configuration generally conform to the Valsalva sinusto enable anchorage of the cardiac-valve prosthesis at the valve site.14. The prosthesis according to claim 13 wherein the anchor portion andthe support portion of the armature are structurally distinct from oneanother.
 15. The prosthesis according to claim 14 wherein the ribsinclude a proximal portion generally shaped to conform to anintraventricular portion of the valve annulus.
 16. The prosthesisaccording to claim 14 wherein the anchor portion includes three sets ofribs, the ribs spaced circumferentially about the armature such thateach set of ribs is adapted to generally conform to each or threecorresponding Valsalva sinuses.
 17. The prosthesis according to claim 13wherein the ribs are made from Nitinol.
 18. The prosthesis according toclaim 17 wherein the ribs are shaped to generally conform to theValsalva sinus.
 19. The prosthesis according to claim 18 wherein theribs are shaped to apply a non-traumatic amount of stress to theValsalva sinus.
 20. The prosthesis according to claim 13 wherein theribs of the anchor portion of the armature have a convex portion that,in a pre-stressed condition, is shaped to position astride a valveannulus site.
 21. A cardiac valve prosthesis comprising: an armatureadapted to anchor the prosthesis at an implantation site generallycorresponding to a location of a natural cardiac valve; a plurality ofprosthetic valve leaflets coupled to the armature and defining a flowduct; and an apron-like portion coupled to the prosthetic valveleaflets, the apron-like portion being shaped to extend radially outwardwith respect to the flow duct and configured to substantially preventflow outside the flow duct when the prosthesis is anchored at theimplantation site.
 22. The prosthesis of claim 21 wherein the apron-likeportion is adapted to channel flow through the flow duct when theprosthesis is anchored at the implantation site.
 23. The prosthesis ofclaim 21 wherein the natural cardiac valve includes an annulus, and theapron-like portion is adapted to be positioned proximal to the annulusand to substantially prevent flow outside the flow duct when sopositioned.
 24. The prosthesis of claim 23 wherein the natural cardiacvalve is the aortic valve and further wherein the apron-like portion isconfigured to be positioned proximal to the annulus and to extendradially from the annulus within the ventricular chamber.
 25. Theprosthesis of claim 21 wherein the armature includes a plurality of ribseach including branched portions shaped to support the apron-likeportion.
 26. A cardiac valve prosthesis adapted for anchorage at animplantation site generally corresponding to a natural cardiac valvehaving an annulus, the prosthesis comprising a valve portion defining aflow duct, and an apron-like portion adapted to be positioned proximalto the annulus and to substantially prevent flow outside the flow ductwhen the prosthesis is anchored at the implantation site.
 27. Theprosthesis of claim 26 wherein the apron-like portion is adapted toflare radially outward with respect to the flow duct and to channel flowthrough the flow duct when the prosthesis is anchored at theimplantation site.
 28. The prosthesis of claim 26 wherein the naturalcardiac valve is the aortic valve and further wherein the apron-likeportion is configured to be positioned proximal to the annulus and toextend radially from the annulus within the ventricular chamber.